1. Field of the Invention
The invention relates to a method of determining a noise component in a signal, and further relates to a circuit arrangement for performing the method.
2. Description of the Related Art
To reduce noise in video signals, circuits are known which are based on the principle of time-recursive filtering. By feedback of an image-delayed output signal to the input of a recursive filter, the noise component is averaged over several image periods and thus reduced.
In this case, a motion detector is customarily provided which controls the value of the feedback video signal in dependence upon motion present in the image. In a known system in accordance with German Patent DE 31 21 597 C2, corresponding to U.S. Pat. No. 4,485,403, a motion signal is gained by subtraction of the undelayed and the delayed video signal. However, similarly as in the input signal, this motion signal is initially beset with noise which detrimentally influences the motion detector. For example, strong noise may be misinterpreted as motion and the recursive filter does not achieve the optimal noise reduction. In order that this is not used for controlling the recursive filter, equally distributed noise is suppressed by means of a threshold circuit and a low-pass filter.